Methods for providing distributed airborne wireless communications

ABSTRACT

Embodiments of methods for providing distributed airborne wireless communications are provided herein. In some embodiments, a method of providing wireless communication services includes: receiving a radio frequency (RF) signal from a first area by a distributed airborne communication payload, wherein the distributed airborne communication payload is comprised of sections located on respective ones of a plurality of airborne platforms; relaying the RF signal along the sections located on different airborne platforms; and transmitting the RF signal to a second area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to United States patent application filedAug. 18, 2014, entitled “APPARATUS FOR DISTRIBUTED AIRBORNE WIRELESSCOMMUNICATIONS”, by Sergey V. Frolov, et al. (attorney docket SP022),United States patent application filed Aug. 18, 2014, entitled “METHODSAND APPARATUS FOR A DISTRIBUTED AIRBORNE WIRELESS COMMUNICATION FLEET”,by Sergey V. Frolov, et al. (attorney docket SP023), United Statespatent application filed Aug. 18, 2014, entitled “DISTRIBUTED AIRBORNEWIRELESS COMMUNICATION SERVICES”, by Sergey V. Frolov, et al. (attorneydocket SP024), United States patent application filed Aug. 18, 2014,entitled “DISTRIBUTED AIRBORNE WIRELESS NETWORKS”, by Sergey V. Frolov,et al. (attorney docket SP025), and United States patent applicationfiled Aug. 18, 2014, entitled “DISTRIBUTED AIRBORNE COMMUNICATIONSYSTEMS”, by Sergey V. Frolov, et al. (attorney docket SP026), each ofwhich are incorporated by reference herein in their entireties.

FIELD

Embodiments of the present invention generally relate to methods andapparatus for airborne wireless communications, and in particular forenabling ground-based wireless communications using unmanned airborneplatforms. Non-limiting examples include providing communication datalinks, voice channels, and various communication services betweenwireless communication devices on the ground and in the air.

BACKGROUND

Global broadband wireless communications have been growing exponentiallyin recent years. Network coverage, however, remains incomplete in manyregions of the world and even in some currently served regions; thusdemand may soon exceed the supply of existing communicationinfrastructure. Current network technologies are generally tooexpensive, ineffective, and slow to respond to growing demand.

In addition, further proliferation of existing ground-based wirelesstechnologies increases radio-frequency (RF) pollution and human exposureto large amounts of RF energy. Many people are concerned that RFexposure might have the potential to cause certain types of cancer andother health problems. Antennas for wireless communications aretypically located on towers, water tanks, and other elevated structures,including building sides and rooftops. RF emissions within 100-150 feetof a cell tower can exceed FCC limits. The standard approach toincreasing wireless capacity by increasing the number of ground-basedantennas per unit area will inevitably lead to an increase in the RFexposure to potentially hazardous levels.

Alternatively, there have been proposals to establish aerial networksthat employ airborne platforms as additional communication hubs. Suchhubs would be stationed at altitudes well above commercial airspace,where the line of sight coverage extends over large terrestrial areasand the average wind-speeds are low. These solutions were proposed asalternatives to satellite communication systems, rather than terrestrialmobile phone communication systems. Closer consideration of earlierproposals and initiatives in this area reveal many shortcomings in thedefined missions, platforms, and supporting technologies as hurdles fortheir successful implementation. As a result, none of these proposalshave been realized in practice so far.

Current broadband services are delivered via wired (e.g., optical fiber)and terrestrial wireless (e.g., cellular) networks with satellite andradio links providing auxiliary coverage beyond the reach of suchnetworks. The inventors have observed that each of these solutions havesignificant constraints limiting their application and leaving many gapsin covered areas.

For example, optical fibers are well suited for fixed high-capacitylinks between high-usage points including continents, cities, metro-areanetworks, and so on. However, they require physical installation, whichis expensive and may not always be practical. In addition, opticalfibers are not appropriate for mobile end users.

Terrestrial cellular wireless networks are well suited for local areadeployments. They are relatively inexpensive, as compared to opticalfiber networks, and are the technology of choice in new and emergingmarkets where the physical infrastructure is limited. Terrestrialcellular wireless networks are appropriate for fixed and mobile usersand may be interfaced to wired networks. However, as discretecomponents, they are range limited and have finite bandwidth. To meet anincreasing customer demand, new towers are added to increase thecoverage density, while reducing their range to enable increasedfrequency reuse.

Satellite links can provide additional coverage to remote andunderserved regions, but they operate at RF frequencies different fromthose of terrestrial wireless networks, have low signal strength andrequire different hardware. In addition, communication satellites areextremely expensive, experience signal delays, and have bandwidthlimitations.

Thus, the inventors believe that there is a need for an improved andmore effective communication system architecture.

SUMMARY

Embodiments of methods for providing distributed airborne wirelesscommunications are provided herein. In some embodiments, a method ofproviding wireless communication services includes: receiving a radiofrequency (RF) signal from a first area by a distributed airbornecommunication payload, wherein the distributed airborne communicationpayload is comprised of sections located on respective ones of aplurality of airborne platforms; relaying the RF signal along thesections located on different airborne platforms; and transmitting theRF signal to a second area.

Other and further embodiments of the present invention are describedbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention, briefly summarized above anddiscussed in greater detail below, can be understood by reference to theillustrative embodiments of the invention depicted in the appendeddrawings. It is to be noted, however, that the appended drawingsillustrate only typical embodiments of this invention and are thereforenot to be considered limiting of its scope, for the invention may admitto other equally effective embodiments.

FIG. 1 depicts a schematic view of an airborne communication system inaccordance with some embodiments of the present invention.

FIG. 2 depicts a schematic view of an unmanned aerial vehicle (UAV)suitable for use in an airborne communication system in accordance withsome embodiments of the present invention.

FIG. 3 depicts a schematic view of some of the major electronicscomponents on board of a UAV suitable for use in an airbornecommunication system in accordance with some embodiments of the presentinvention.

FIG. 4 depicts a representation of a divided communication payloaddistributed among different UAVs in an airborne communication system inaccordance with some embodiments of the present invention.

FIG. 5 depicts a schematic view of a UAV having an onboard air-to-user(ATU) antenna to produce a directed RF beam in accordance with someembodiments of the present invention.

FIG. 6 depicts a graph of the field intensity distribution in asymmetric cone-shaped beam versus the angle of the beam in accordancewith some embodiments of the present invention.

FIG. 7 depicts a schematic view of a UAV platform equipped with one ormore RF antennas which produce multiple RF beams to establish multipleATU ground cells and ATU air cells in accordance with some embodimentsof the present invention.

FIG. 8 depicts a schematic view of a UAV fleet comprising a plurality ofUAV platforms each equipped with an RF antenna to produce respective RFbeams which establish multiple ATU ground cells and ATU air cells inaccordance with some embodiments of the present invention.

FIG. 9 depicts a schematic view of a UAV fleet that providescommunication services in accordance with some embodiments of thepresent invention.

FIG. 10 depicts a ground projection of a cellular map composed ofapproximately similarly sized and shaped communication cells inaccordance with some embodiments of the present invention.

FIG. 11 depicts a ground projection of a cellular map composed ofapproximately similarly sized hexagonal communication cells inaccordance with some embodiments of the present invention.

FIG. 12 depicts a ground projection of a cellular map composed ofapproximately similarly sized rectangular communication cells inaccordance with some embodiments of the present invention.

FIG. 13 depicts a ground projection of a cellular map composed ofirregularly sized and shaped cells in accordance with some embodimentsof the present invention.

FIG. 14 depicts a schematic view of several airborne platforms capableof carrying communication payloads and performing functions necessaryfor enabling an airborne wireless communication network in accordancewith some embodiments of the present invention.

FIG. 15 depicts a schematic view of a communication subsystem forestablishing air-to-air (ATA) links between individual UAVs or otherairborne platforms in an airborne wireless communication system inaccordance with some embodiments of the present invention.

FIG. 16 depicts a schematic view of a UAV fleet as a part of adistributed airborne communication system which includes UAVs thatestablish ATA links maintained between nearest neighbors in the UAVfleet in accordance with some embodiments of the present invention.

FIG. 17 depicts a schematic view of a ground-based gateway station usedto establish broadband communication channels with a UAV fleet inaccordance with some embodiments of the present invention.

FIG. 18 depicts a schematic view of an airborne wireless broadbandcommunication system in accordance with some embodiments of the presentinvention.

FIG. 19 depicts a schematic view of a communication system whichincludes a ground station, a UAV fleet, and a region with ATU cells inaccordance with some embodiments of the present invention.

FIG. 20 depicts a schematic view of a communication system whichincludes a communication satellite, a UAV fleet, and a region mappedwith ATU cells in accordance with some embodiments of the presentinvention.

FIG. 21 depicts a schematic view of a distributed airborne communicationpayload for a UAV fleet in accordance with some embodiments of thepresent invention.

FIG. 22 depicts a schematic view of a distributed communicationsubsystem which may be used to implement RF-based communication links inaccordance with some embodiments of the present invention.

FIG. 23 depicts a schematic view of a payload control subsystem for adistributed airborne communication system in accordance with someembodiments of the present invention.

FIG. 24 depicts a schematic view of a schematic view of ATA linkequipment subdivided into two sections for internal and externalcommunications, respectively, in accordance with some embodiments of thepresent invention.

FIG. 25 depicts a schematic view of a distributed airborne communicationnetwork comprising an end-user node, an airborne node, a gateway node,an external node, a cell tower node, and a satellite node in accordancewith some embodiments of the present invention.

FIG. 26 depicts a schematic view of a distributed airborne communicationnetwork comprising a multitude of airborne nodes, and a multitude ofend-user nodes, in accordance with some embodiments of the presentinvention.

FIG. 27 depicts a schematic view of an airborne node design topologywhich includes three types of payload bearing UAV platforms: a relayplatform, a transmitter platform, and a receiver platform, in accordancewith some embodiments of the present invention.

FIG. 28 depicts a schematic view of an airborne node design topologywhich includes two types of payload bearing UAV platforms: a masterplatform and a plurality of slave platforms, in accordance with someembodiments of the present invention.

FIG. 29 depicts a schematic view of a UAV fleet comprised of a pluralityof UAVs in accordance with some embodiments of the present invention.

FIG. 30 depicts a schematic view of a flight formation pattern for a UAVfleet in accordance with some embodiments of the present invention.

FIG. 31 depicts a schematic view of a several flight formation patternsfor UAV fleets in accordance with some embodiments of the presentinvention.

FIG. 32 depicts a schematic view of a distributed communication system,comprising a fleet of two UAVs that service a single communication cell,in accordance with some embodiments of the present invention.

FIG. 33 depicts a schematic view of a distributed communication system,comprising a fleet of two UAVs that respectively service two differentcommunication cells, in accordance with some embodiments of the presentinvention.

FIG. 34 depicts a schematic view of a distributed communication system,comprising a fleet of two UAVs that respectively service two differentcommunication cells, in accordance with some embodiments of the presentinvention.

FIG. 35 depicts a flow chart of a method for communicating using adistributed airborne wireless system in accordance with some embodimentsof the present invention.

FIG. 36 depicts a flow chart of a method for providing a distributedairborne wireless communication node in accordance with some embodimentsof the present invention.

FIG. 37 depicts a flow chart of a method for providing a distributedairborne wireless communication node in accordance with some embodimentsof the present invention.

FIG. 38 depicts a chart of additional actions, which could complimentmethods shown in FIGS. 36 and 37, in accordance with some embodiments ofthe present invention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The figures are not drawn to scale and may be simplifiedfor clarity. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of exemplaryembodiments or other examples described herein. However, it will beunderstood that these embodiments and examples may be practiced withoutthe specific details. In other instances, well-known methods,procedures, components, and/or circuits have not been described indetail, so as not to obscure the following description. Further, theembodiments disclosed are for exemplary purposes only and otherembodiments may be employed in lieu of, or in combination with, theembodiments disclosed.

One particularly useful application of this invention is to interfacewith, augment, or replace existing and future terrestrial wirelessnetworks that rely on cell towers. The envisioned network employs afleet of high-altitude solar-, or hybrid-, powered fixed-wing airborneplatforms as communication hubs. Such a system is able to use standardterrestrial wireless frequencies and protocols, simplifying integrationwith conventional wireless base stations and user equipment,respectively. It may operate either as a stand-alone system, or inconjunction with other terrestrial and satellite-based communicationsystems. In addition, the same system architecture may be used toprovide one or more of fixed link communication services, emergencycommunications, secure communication channels, radio and/or televisionbroadcast services, internet and cloud-based computing services,streaming, and other broadband communications services.

The platforms will generally maintain position at altitudes betweenabout 15 and 30 km and can be capable of supporting communication linksyear-round. Unmanned Aerial Vehicles (UAVs) are unpiloted aircraft thatare either controlled remotely or flown autonomously alongpre-programmed flight plans. They are preferred platforms forimplementing this airborne communication system, although other airbornevehicles may be also used under appropriate conditions, e.g.,lighter-than-air aircraft. UAVs are commonly categorized based on theirdesign and performance specifications spanning the range from miniaturelow altitude aircraft to larger High Altitude Long Endurance (HALE)vehicles. HALE UAVs are particularly attractive for this application forreasons described below.

The inventors have observed that previously proposed aerialcommunication networks without exception underestimated communicationpayloads and airframe requirements to physically and operationallysupport such payloads with the level of power generation requiredyear-long for 24 hour continuous operation. The inventors haverecognized these shortcomings, analyzed in detail the requirements forthe mission, and identified significant challenges in airframe design,power generation, and energy storage, which are difficult to overcomewith conventional solutions and approaches suggested thus far and whichcan be mission limiting, if not prohibitive.

As will be made clear from the teachings provided herein, one or more ofseveral operational advantages that embodiments of this invention mayprovide as compared to existing terrestrial and satellite networks,including without limitation:

-   -   a) Low RF exposure: Airborne wireless system provide a much more        uniform distribution of RF power on the ground in comparison to        ground-based antennas. Furthermore, airborne communication links        are usually in the line-of-sight, which reduces multipath        interference. As a result, the average and maximum RF power        levels on the ground for the airborne system can be        substantially lower, virtually eliminating the risk of hazardous        RF exposure.    -   b) Large-area Coverage: UAV's location means that communication        links experience relatively little rain attenuation compared to        terrestrial links over the same distance. At the shorter        millimeter-wave bands this can yield significant link budget        advantages within large cells.    -   c) Traffic responsivity: The invention is well suited to provide        centralized adaptable resource allocation, i.e. flexible and        responsive frequency reuse patterns and cell sizes unconstrained        by the physical location of base-stations. This adaptability can        provide significantly increased overall capacity as compared to        current fixed terrestrial mapping.    -   d) Low cost: Airborne networks will be considerably cheaper to        procure and launch than a geostationary satellite or a        constellation of low earth orbit (LEO) satellites. It can also        be cheaper to deploy than a terrestrial network with a large        number of base-stations. The UAVs will also be designed and        sized for manufacturing.    -   e) Incremental deployment: Airborne services can be introduced        with individual UAVs and then expanded as greater coverage        and/or capacity is required. This compares favorably with a LEO        satellite network, which requires a large number of satellites        for continuous coverage. Terrestrial networks also require a        significant number of base-stations to be fully functional.    -   f) Rapid deployment: It is feasible to design and deploy        UAV-based service quickly. Satellites, typically take years from        initial procurement through launch to on-station operation, with        payloads frequently obsolete by the time of launch. Similarly,        terrestrial networks require time-consuming planning and civil        works. UAVs, on the other hand, can be launched and placed on        station within a matter of days, or even hours, enabling a rapid        roll-out of services to providers keen to get in business before        their competition. Rapid deployment will also be key for        emergency scenarios such as natural disasters, military        missions, restoration when terrestrial networks experience        failure and anticipated overload due to large concentrations of        transient users, e.g., at major events.    -   g) Maintenance and upgrades: A fleet of UAVs may operate for        extended periods—weeks, months, or even years. Unlike        satellites, UAVs can land for maintenance or upgrades or be        replaced on station with no service disruption.    -   h) Low Environmental Impact: HALE UAVs have on-board renewable        power generation, including solar power systems. Complementary        remote power delivery can be also added to ensure reliable and        continuous operation. Additional environmental benefits arise        from elimination of large numbers of terrestrial towers and        associated infrastructure.

In accordance with embodiments of the present invention, airbornesystems are provided for enabling wireless communications services amongend users on the ground and in the air. The systems generally comprise afleet of unmanned airborne vehicles (UAVs) and an optional base-stationlocated on the ground. UAVs carry a distributed payload that compriseswireless communication equipment. In some embodiments of the presentinvention, an apparatus, such as an airborne communication system 100schematically shown in FIG. 1, may comprise a plurality of UAV platforms110 (e.g., a fleet), an optional ground base station 120, configured tocommunicate with a plurality of mobile radio transceivers, as describedin greater detail herein. Mobile radio transceivers may be airborne orlocated on the ground. For example, the mobile radio transceivers may becellular phones held and used by individuals 130 on the ground 140 orcarried on board of passenger airplanes 145, as shown in FIG. 1.Distances between different UAVs may vary and depend on theircommunication capabilities and requirements for communication servicesthey provide. In general, some UAVs within the fleet may fly in closeproximity to each other, so that the distance between them may besmaller than the distance to the service area (e.g. ground 140).Communication services provided by the airborne communication system 100may be continuous or substantially continuous, e.g., 24 hours a day, 7days a week, year round, etc. Alternatively, these services may beintermittent or temporary, e.g., one or more of only daytime operations,emergency support, peak demand services, etc.

UAV platforms 110 may be similar or nearly identical to each other.Alternatively, these platforms may have varying designs and differingoperational characteristics. A UAV 200 suitable for this missioncomprises an airframe 210, a propulsion subsystem 220, a power trainsubsystem 230, and an electronics subsystem 240, as shown in FIG. 2. Theairframe 210 enables aerodynamically efficient long-endurance UAVflight, minimizing the power necessary to maintain the level flight andto maneuver (e.g., to make turns). This is accomplished by providing,among other things, wings with low wing loading (<5 kg/m²), large wingsurface (for sufficient lift and solar power generation as determined byweight and power requirements of a UAV), airfoil cross-section with highlift coefficient (>1-1.5), high wing aspect ratio (>10), low weightcomposite construction (e.g. based on carbon, glass or polymer fibers)and so on. Propulsion subsystem 220 provides means for acquiring andmaintaining air speed (for level flight, ascent, descent, turns andother maneuvers) and includes at least a motor and a propeller. Thepower train subsystem 230 provides electrical power to the propulsionsubsystem 220 and electronics subsystem 240. It may be a hybrid powersystem based on various renewable and remote energy sources, includingsolar energy, wind energy, thermal energy, fuel cells, combustionmotor-generator sets, microwave energy and others. The solar energy maybe harvested for example using a photovoltaic (PV) power system.Specific non-limiting embodiments of the UAV 200 utilizing renewableenergy sources may be found, for example, in U.S. Pat. No. 8,448,898,issued May 28, 2013 to Frolov, et al., and entitled, “Autonomous SolarAircraft”. In addition, energy may be stored in the form of potentialenergy by increasing UAV's altitude. The electronics subsystem 240enables flight control and operational functionality for wirelesscommunications in the airborne communication system 100.

The fleet of UAV platforms 110 may operate at different altitudesranging from sea level to about 30 km. An optimum altitude depends onvarious factors including weather conditions, local regulations foraircraft flight, aircraft capabilities and application requirements.Weather conditions are typically optimal at altitude of about 20 km,which is characterized by little cloud cover and minimal average windspeeds. However, the wind speed may still be substantial and exceed 100km/h. The propulsion system should be capable to generate sufficientpower and thrust to allow an airframe acquire airspeeds greater thanwind speeds at operating altitudes (e.g., >100 km/h). High altitudeoperations also make it harder to generate lift, requiring larger wingsurface for fixed-wing aircraft and larger volumes for lighter-than-airaircraft and further emphasizing the need for relatively light-weightairframes and payloads.

In some embodiments, as shown schematically in FIG. 3, some of the majorelectronics components on board of a UAV 300, which could be used in theairborne communication system 100, may include flight controlelectronics 310 and payload modules. Examples of payload modulesinclude, payload control electronics 320 (e.g., a payload controlelectronics module), air-to-user (ATU) link communications electronics330 (e.g., an ATU link module), air-to-air (ATA) link communicationselectronics 340 (e.g., aa ATA link module), and air-to-ground (ATG) linkcommunications electronics 350 (e.g., an ATG link module). The flightcontrol electronics 310 may be powered by the power train subsystem 230and provide capabilities for maneuvering of a UAV and maintainingvarious flight patterns. Among other elements, it may include anauto-pilot for UAV flight control and a programming interface for manualor remote input of flight parameters.

The communication payload components are required for providingcommunication services, rather than flight control functionality(although they may indirectly affect flight patterns and UAV flightcharacteristics). An airframe should have available areas andcompartments for payload placement and attachment. The payloadmodules—i.e., the payload control electronics 320, ATU linkcommunications electronics 330, the ATA link communications electronics340, and the ATG link communications electronics 350—represent the mainelements of the wireless communication equipment payload 360.Communication equipment may support one or more of at least threedifferent types of communication links or channels: (1) Air-to-User(ATU) links between UAVs and mobile users/cell phones, (2) Air-to-Air(ATA) links between different UAVs, and (3) Air-to-Ground (ATG) linksbetween UAVs and terrestrial gateway base stations. Each link mayutilize a number of suitable communication formats, includingfrequency-domain multiple access (FDMA), time-domain multiple access(TDMA), code-domain multiple access (CDMA), and combinations thereof.

In general, the airborne communication system 100 may also includepiloted aircraft, which may be used to support, replace, and/or addfunctionality to the unmanned airborne platforms. The piloted aircraftmay be able to access restricted regions inaccessible by unmannedplatforms due to local regulations, weather, or lack of renewable energyresources. Piloted aircraft may serve as a backup in emergencysituations or peak demand conditions. In addition, piloted aircraft mayprovide secondary energy resources to other airborne platforms in thefleet, e.g., in the form of wireless RF power transfer betweenplatforms, direct contact battery charging, refueling, and so on.

The combined power and weight requirements of such a payload may be toodemanding, excessive, and overwhelming for a single UAV platform.Embodiments of the present invention address this problem by splittingthe payload into smaller constituent parts, thus distributing it amongdifferent UAVs in the airborne system, as shown in FIG. 4. In this case,a fleet 400 comprising a number (N) of UAVs (400 ₁ through 400 _(N)) isused to carry a communication payload 460. Some or all of thecommunication payload 460 components (i.e., modules) may be subdivided,so that each subdivision (i.e., module section) is carried by anindividual UAV platform. Each subdivision or section of the payload maybe housed in a single or multiple housings to be mounted within a UAVplatform. Thus, a single section housing may carry parts of multiplepayload modules. For example, the UAV 400 _(i) carries payloadsubdivisions, or sections, of the payload control electronics 420 _(i),the ATU link equipment 430 _(i), the ATA link equipment 440 _(i), andthe ATG link equipment 450 _(i), where the index i ranges from 1 to N.

The payload components may be distributed evenly or unevenly across theUAV fleet. Distribution of the payload increases system's redundancy,lowers its costs, and simplifies maintenance. Uneven distribution mayhelp optimize payload performance, minimize overall power consumption,and increase the system's capabilities. A lone UAV with its respectivepayload subdivision may not be able to perform the full range ofcommunication services and network operation. Instead, a minimum numberof UAVs greater than one may be necessary to enable such an airbornecommunication system.

Different types of ATU links may be provided including point-to-pointlinks, multiple access links, one-way and two-way communication links,audio and video broadcast links for radio and television,multicast/broadcast links, data and voice communication links, textmessaging links, and so on. For example, two-way ATU links may beprovided supporting data and voice communications via cellular phones.Such ATU links can be provided by airborne high-gain directionalantennas operating in the RF range of about 0.5 to about 5 GHz,compatible with the existing cell phone technologies. The antennas canbe one or more of horn antennas, analog phased arrays, digital phasedarrays, and others. The serviced region on the ground can be segmentedinto communication service cells (e.g., communication cells), so thatthe same RF frequencies or channels can be reused within differentsegments, or cells. The directional antennas may provide different RFbeams to cover the communication cells. Multiple access ATU links may beestablished, for example, to provide cellular communication services forend-users with hand-held mobile wireless devices, such as cell phones.

ATA links can be provided by either directional RF antennas orfree-space optical interconnections, e.g., using telecom-grade lasersoperating at about 1300 to about 1600 nm. The ATA links may preferablybe point-to-point links, although multiple access ATA links may also beused, especially between UAVs in close proximity. This approach canenable high bandwidth (e.g., >40 Gbps) and interference free connectionsbetween different platforms in the air. ATA links may provide theshortest and cheapest available communication path between differentusers on the ground. ATG links may be point-to-point links and can beprovided using airborne and ground based high-gain directional microwaveantennas, e.g., tracking phased array antennas operating in the about 10to about 100 GHz range. This approach enables a relatively highbandwidth (e.g., >1 Gbps/link) and interference free connections betweenplatforms in the air and ground based gateway stations. The gatewaystations also provide connections and entry points to existing wiredservices, such as terrestrial telecommunication networks and theinternet.

ATU links establish wireless connections to the network users below theairborne platforms. An ATU link may be produced by a single or severalUAV platforms using RF beams at one or multiple channel frequencies. Insome embodiments, and as shown in FIG. 5, a single UAV 500 utilizes anonboard ATU antenna 510 to produce a directed RF beam 520 carryingcommunication signals (e.g., RF signals). The RF beam 520 may have atransmission direction pointing towards the ground below and cover anarea on the ground 550. The area is defined by the RF beam 520 spreadproduced by the onboard ATU antenna 510 and may be referred to as an ATUground cell 530. Ground-based end-users inside the same ATU ground cellmay be served by the same RF beam. In addition, an ATU air cell 540 maybe defined as marked and bounded volumetrically by the spread of the RFbeam 520. Airborne end-users, such as those for example onboard of anairplane 560, may be serviced by the RF beam 520 while passing throughthe ATU air cell 540. The ATU ground cell and the ATU air cell are eachalso referred to as a communication cell.

In the case of a symmetric cone-shape beam, the field intensitydistribution in the beam versus the angle or direction (e.g., theangular field intensity distribution) may be approximated by the curve600 shown in FIG. 6. The center of the beam is defined by the verticalaxis 610, where there is a maximum in the field intensity. The angle isdefined in FIG. 5 as the angle between the center of the cone 570 and anRF ray 580. The outer boundaries of the beam 630 may then be defined bythe minimum level of the field intensity acceptable for establishing theATU link or its relative strength with respect to other interferingbeams, e.g., a half-maximum intensity level 620 as shown in FIG. 6. As aresult, the angular spread 640 of the beam approximated by the curve 600is given about 2Theta₀ where Theta₀ is defined as the angle whichcorresponds to the minimum level of the field intensity acceptable forestablishing the ATU link or its relative strength with respect to otherinterfering beams (e.g., the half-maximum intensity level 620 in FIG.6). For a given altitude H, such a beam will produce an ATU ground cellwith a diameter of about 2Theta₀H. In general, the RF field intensitydistribution may be variable. For example, a digital phased arrayantenna may be able to produce RF beams of various shapes and sizes. Asa result, communication cell size and shape may also vary. This featurecan be used effectively to optimize operations of an airborne wirelesssystem. In addition, RF beams may be reshaped to produce minimuminterference in communication cells produced by other RF beams bygenerating nulls in the field intensity distribution at correspondinglocations.

The above description of an embodiment refers to both modes of operatinga communication channel (i.e., transmission and reception). The onboardATU antenna 510 may be used to transmit signals, thus providing an ATUdownlink, to end users in the ATU ground cell 530 and in the ATU aircell 540. Similarly, the onboard ATU antenna 510 may be used to receivesignals, thus providing an ATU uplink, to end users located in the ATUground cell 530 and in the ATU air cell 540. In this case RF beamsemitted from these cells in the upward transmission direction towards aUAV (or UAVs) may be received by the onboard antenna 510. Thus twodifferent RF beams may be used for establishing an ATU link: first—an RFbeam transmitted by an ATU equipment from a UAV towards a communicationcell (e.g., a first beam), and second—an RF beam emitted by from acommunication cell towards a UAV and received by an ATU equipment (e.g.,a second beam). Signal transmission and reception may occur on the sameUAV or different UAVs, at different times or simultaneously. In thelatter case, the signals may be transmitted and received at differentfrequencies, channels or RF bands to avoid interference. Alternatively,two different antennas may be used for simultaneous transmission andreception of RF signals within the same ATU link and/or ATU cell. ATUlink communications may also include control and setup communicationsbetween the ATU link equipment and end-user's wireless communicationequipment. These communications may in turn include end-user discovery,identification and registration in the communication network provided bythe airborne communication fleet, as well as assignment of communicationchannels (both for receiving and transmitting signals) to particularend-users, mitigation of interference from obstacles and othertransmitters, hand-offs between different communication cells, and soon.

In some embodiments, and as shown in FIG. 7, a UAV platform 700 isequipped with one or more RF antennas 710, which produce one or more RFbeams 720, (i ranges from 1 to N, where N is the total number of RFbeams). As used herein, a “platform”, or a “UAV platform”, refers to anunloaded (empty) unmanned airborne vehicle used as a quasi-stationary“platform” for a communication payload or its parts. (In contrast, a“UAV” may refer to either a UAV platform without a payload or a UAV witha payload onboard, depending on a context.). As a result, several ATUground cells 730 _(i)-730 _(N) and ATU air cells 740 ₁-740 _(N) may beestablished and supported by the UAV platform 700. The corresponding ATUlinks may be operated in the same or different RF bands. Operation oftwo neighboring ATU cells at different frequencies or channels preventsinterference and allows an overlap between these cells (see for examplecells 730 ₁ and 730 ₂). Depending on the size of the cells, which mayrange from tens or hundreds of kilometers down to several meters, theymay be categorized as super-cells (about 10-100 km), macro-cells (about1-10 km), mini-cells (about 0.1-1 km), micro-cells (about 10-100 m), orpico-cells (about 1-10 m), respectively. A larger cell size typicallymeans a larger number of customers and thus a higher net bandwidthdemand, which in turn requires a heavier payload and higher powerconsumption. Therefore, while a number of smaller cells (micro- andpico-cells) may be supported by a single UAV platform as described inFIG. 7, larger cells (super- and macro-cells) may require more than asingle platform because of their more demanding requirements.

In another embodiment shown in FIG. 8, an airborne fleet, such as a UAVfleet 800 (also referred to as a set, swarm, group, flock, cluster,convoy, collection, or constellation) consisting of N number of UAVplatforms 800 ₁-800 _(N) provides communication services in the spaceunderneath, where each UAV platform 800 _(i) carries an antenna 810_(i), producing an RF beam 820 _(i), and projecting ATU ground cell 830_(i) and ATU air cell 840 (where i ranges from 1 to N). Antennas 800₁-800 _(N) may operate at the same or different frequencies, channels,or RF bands. The UAV fleet 800 may provide the same capabilities for itsend users as the single UAV platform 700. However, it allows thecommunication payload to be split into smaller parts and makes theairborne communication service more robust, scalable, and sustainable.For example, the RF antennas 810 ₁-810 _(N) are the elements of the samecommunication payload, each carried by a separate UAV platform 800 ₁-800_(N) respectively. In addition, this approach allows each UAV platformto hover and circle directly above their corresponding ATU ground cells.Airborne platforms may maintain their position by hovering or circlingabove predetermined positions specified in GPS coordinates. This resultsin a vertical line-of-sight (LOS) between a UAV platform and anend-user, which minimizes the transmission distance, scattering losses,and multipath fading. ATU links, which are angled with respect to thevertical direction normal to the ground surface, experience higher lossand therefore may require larger RF power for transmission andreception.

In another embodiment shown in FIG. 9, a UAV fleet 900 consisting of Nnumber of UAV platforms 900 ₁-900 _(N) provide communication services inthe space underneath, where each UAV platform 900 _(i) carries anantenna 910 _(i), producing an RF beam 920 _(i), and projecting ontocommon ATU ground cell 930 and ATU air cell 940 (where i ranges from 1to N). Antennas 910 _(i) may operate at different frequencies, channels,or RF bands to avoid interchannel interference, in effect increasingtraffic capacity in the ATU ground cell 930 (and ATU air cell 940) byfrequency multiplexing. Alternatively or additionally, they may sharesome or all of their operational frequencies and use other multiplexingapproaches: (a) time multiplexing, (b) polarization multiplexing, (c)spatial/positional multiplexing, or the like. Time multiplexing may beachieved by allotting special time frames in an ATU channel for each UAVplatform 900 _(i) to transmit and/or receive communication signals.Polarization multiplexing may be accomplished by configuring theantennas 910, to receive and transmit polarized RF radiation inorthogonally polarized (i.e., non-interfering) states. Spatial andpositional multiplexing may be realized by using multiple-inputmultiple-output (MIMO) approaches for increasing channel capacity. Anend-user within the ATU ground cell 930 and the ATU air cell 940 may beable to use available ATU links, channels and frequencies from one ormore UAV platforms 900 ₁-900 _(N) simultaneously, concurrently,constantly or intermittently.

The airborne communication system that is in part embodied by the UAVfleet 900 in FIG. 9 relies even more on a concept of subdividing acommunication payload into smaller and more manageable parts. Thisdistributed payload approach is distinctly different from prior art,where the conventional wisdom has been to use a single UAV platform andpush its performance limits to cover and serve the largest ground areapossible. The inventors see their new approach as more advantageous forseveral reasons. From the UAV platform perspective, it is easier andcheaper to design, manufacture, and operate smaller UAVs. The UAVairframe weight scales approximately as the cube of its size, while thesize (wing span) increases as the square root of the wing area.Therefore, for the same wing area (and thus available solar power) 10smaller UAVs will have the combined weight of less than 3 times theweight of a single large UAV (˜(10)^(3/2)/10). The wing loading is thusmuch smaller for smaller UAVs, which means they are more aerodynamicallyefficient. It is also possible to further reduce total power consumptionin a UAV fleet by dynamic task scheduling between different UAVs,arranging UAVs in flight formations for improved aerodynamics, wirelessenergy exchange between different UAVs, and so on. As a result, it takesmuch less power for a fleet of relatively small UAVs to maintain flightand there is more power available for the payload in comparison to alarge single UAV.

From the system perspective, the distributed payload approach increasessystem reliability and introduces built-in redundancy. If one small UAVplatform fails, the remaining platforms may fill in and providetemporary or permanent back-up operations for the missing UAV, so thatthe system will continue to function normally without any interruptionsfor end-users. It is also easier to maintain smaller UAV operations.They can be brought down and landed on a periodic maintenance schedulefor upgrades, repairs and refueling if necessary, which much moredifficult and challenging to do with a large single platform. Acommunication system with a distributed airborne payload is veryscalable, so that the number of UAVs required for providingcommunication services may be changed and adjusted depending on thedemand for services, seasonal changes or atmospheric conditions. Thisstrategy ensures a good match between the deployed airborne resources(supply of services) and the required bandwidth and area coverage(demand for services).

From the end-user perspective, this invention discloses a new way toprovide communications to personal mobile devices (like cell phones),which is better than either current terrestrial systems, satellite-basedsystems, or any of the previously proposed airborne systems. The ATUlinks as shown in the described embodiments are compatible with existingcellular technology, so that end-users may conveniently use theirexisting devices to order to become a part of this airbornecommunication network. The distributed payload approach makes this notonly feasible, but also safer. In case of an accident or emergency, asmaller UAV may be brought down much safer and with less risk comparedto any larger UAV. Also, a larger UAV constantly hovering above in thesky is much more visible than a small UAV and may represent an eye soreand cause for concern to the general public.

The airborne fleet is configured to provide a plurality of communicationcells (e.g., ATU cells) by projecting a plurality of RF beams to createa communication cell be each respective RF beam. The plurality ofcommunications cells may each be substantially the same (e.g., havesubstantially equal size and/or shape), or at least one communicationcell may be different than others of the plurality of communicationcells (e.g., at least one communication cell has a size and/or shapethat is different than the other communication cells).

For example, FIGS. 10-13 show exemplary embodiments for cellular mappingof an airborne wireless service area, which characterize another part ofthe distributed airborne communication system. FIG. 10 shows the groundprojection of a cellular map 1000, which is composed of approximatelysimilarly sized (e.g., substantially equally sized) and shapedcommunication cells. Each cell may be produced and serviced by one ormore UAV platforms. A single UAV platform may produce one or more ofthese cells. The shapes of corresponding ATU ground cells and ATU aircells are circular and conical, respectively. Neighboring cells mayoverlap, so that for example cells 1010 and 1020 may have an overlapregion 1015. In order to avoid interference in region 1015, the channelsused in cells 1010 and 1020 may differentiate from each other by usingdifferent frequencies, polarizations, spatial positioning, and so on. Inaddition, each cell may be further segmented in subcells, regions,sectors, and segments with differing characteristics in order toincrease frequency spectrum reuse.

Ignoring the overlap regions, the same or similar cellular map may berepresented by a map 1100 in FIG. 11, which comprised of hexagonalcells. In this example, three types of cells are identified as 1110,1120, and 1130, corresponding to different frequency ranges. These cellsmay be repeated in a non-interfering pattern as shown in FIG. 11 to fillan entire region without gaps in coverage. Unlike terrestrial cellularmaps, these maps produced by airborne communication platforms are notaffected by radio wave propagation and scattering near ground surface.Consequently, they provide much more even signal intensity distributionand enable more effective planning, allocation and forecasting forcommunication services.

A particular characteristic of cellular mapping that have not beenpreviously realized or even identified in prior art, particularly inregard to existing terrestrial wireless systems, is the ability tocontrol the size, shape, and layout of cellular mapping and each givencell inside of it. The RF signal intensity pattern and distribution interrestrial systems are fixed and given by the locations of cellularcommunications towers and other wireless network antennas andtransceivers. In the present invention, the communication cell shape,size, and position is not fixed and may be varied or maintained, becauseit is mostly determined by the emission characteristics of the RFantennas onboard of the UAV platforms, which may be controlled. Forexample, an antenna may be set to point in a new direction (e.g., atransmission direction), which will change the position of acorresponding communication cell to a new location. A phased arrayantenna may be used to produce a beam or multiple beams with shapes andsizes that can be changed on command to fit specific needs of anapplication at that locale. A digital phased array antenna may be usedto change the size, shape, or location of the RF beam and correspondingATU cells electronically without moving any relevant mechanical parts.Thus, in some embodiments, at least one communication cell can have atleast one of a fixed size, shape, or position. And, in some embodiments,at least one communication cell has at least one of a variable size,shape, or position.

In another embodiment of the present invention, FIG. 12 shows a cellularmap 1200 comprising rectangular-shaped ATU cells. Four types of suchcells 1210, 1220, 1230, and 1240, each operating in respectively fourdifferent frequency spectral ranges, may be used to effectively coverarbitrary size region in a non-interfering pattern, i.e., a patternwhich doesn't have neighboring or overlapping region with operating inthe same frequency range. Additional frequency regions may be addedand/or the cells may be subdivided into smaller divisions in order toincrease frequency utilization and overall system capacity. The cells inFIG. 12 may also have different sizes and shapes, while preserving thesame overall topology. Also, the cellular map may be made up ofcompletely irregular and dissimilar cells. FIG. 13 shows a cellular map1300 comprised of several irregular cells. For example, FIG. 13illustrates neighboring cells 1310 and 1320, which are dissimilar insize and shape.

Such cellular maps are impossible to achieve with regular terrestrialwireless systems. However, they may be advantageous to minimizecommunication hand-offs between different cells. When an end-usercrosses from one cell to another, a communication system must perform ahand-off procedure, which may take additional resources and affectservice quality. This situation typically occurs along roads andhighways, due to vehicular traffic in these areas. A cellular map may bedesigned to better fit the pattern of end-user movements to minimize thehand-offs, e.g., by referencing the map against road maps and end-usertraffic patterns. This can be accomplished in some embodiments of thisinvention by using an airborne communication system with UAV platformequipped with phased array antennas, which in turn can control andmaintain an arbitrary cellular map, cell shapes, sizes, boundaries,and/or their positions with respect to one or more reference points onthe ground, e.g., landmarks such as natural features and man-madestructures. For example, in some embodiments, the communication cellboundaries may be aligned with landmarks on the ground. In addition, thecellular map may be altered, changed, and reconfigured at any time inresponse to changes in customer demand, internal network status,external factors, and other considerations. Furthermore, instead ofmaintaining a cellular map that is fixed and referenced with respect tospecific locations or markers on the ground, it is possible to createand maintain a floating cellular map that may be either constantly oroccasionally moving with respect to end-users on the ground. In thiscase other reference points for cellular mapping may be used, such asfor example the airborne platforms themselves or virtual referencepoints maintained and calculated by the software running the operatingsystem of the airborne network.

The ATU link may be characterized by the transmission and receptionranges, i.e. the maximum distances for transmitting signals to andreceiving signals from an end-user, respectively. These ranges ingeneral depend on the transmitted signal power, atmospheric conditions,transmission format and rate, multipath interference and other factors.The advantage of an airborne communication system is that it minimizesthe effect of the multipath interference, which represents one of thedominant factors in signal loss in terrestrial wireless communicationsystems. For an airborne system the average transmission and receptionrange is about equal to the altitude of the airborne system, which maybe in the range of about 17 to about 20 km. This distance may besubstantially smaller than the average distance between differentairborne platforms, which may be in the range of about 10 m to about 10km. In contrast, the communication range in a terrestrial cellularsystem is less than a distance between cellular communication towers,for example, about one half of the average distance between cellularcommunication towers, such as in the range of about 1 to about 5 km.

In accordance with the present invention, FIG. 14 shows exemplaryembodiments of several airborne platforms capable of carryingcommunication payloads and performing functions necessary for enablingan airborne wireless communication network. A platform 1410 is afixed-wing, heavier-than-air UAV comprising at least a fuselage 1411, awing 1412, and a tail 1413 (propellers are not shown). The platform 1410is capable of carrying a payload or parts of a payload inside andoutside of constituent elements of the platform 1410. An RF antenna1415, as a part of the payload, may be mounted to the bottom of afuselage of the platform 1410, or integrated into a skin of the platform1410, as shown in FIG. 14. A platform 1420 is a lighter-than-airaerostat or an airship, which includes at least an airship shell or ahull 1421, propellers 1422, and a tail 1423. An RF antenna 1425 may bemounted to the bottom of the hull or integrated into a shell or cover ofthe hull 1421, as shown in FIG. 14. Both RF antennas 1415 and 1425 maybe used to create one or more directed, arbitrary shaped RF beams fortransmitting and receiving signal from the ground and air space below.Furthermore, a UAV 1430 and an airship 1440 may be equipped withmultiple RF antennas 1435 and 1445, as shown in FIG. 15, to producemultiple RF beams. Each beam may than produce a corresponding ATU cellfor establishing an ATU link. The use of UAVs as the platform forairborne communications is advantageous because of UAV's ability to movequickly and withstand high winds. The use of airships as the platformfor airborne communications may be also advantageous because of theirability to conserve energy in still air and provision of large surfacesavailable for sunlight energy collection. Although in general the use ofUAVs is preferred, there may be situations and conditions where the useof airships is more advantageous. Furthermore, a potentially moreflexible and reliable airborne system may be produced with a combinationof UAV and airship platforms in the same airspace, which could deliveradvantages of both technologies.

In accordance with some embodiments of the present invention, FIG. 15shows a communication subsystem 1500 for establishing ATA links betweenindividual UAVs or other airborne platforms in the airborne wirelesscommunication system. The communication subsystem 1500 is used tocommunicate, exchange data, and relay signals between two or moreaircraft. The communication subsystem 1500 provides wireless connectionsbetween parts of a distributed communication payload. Thus, each UAV ina functional distributed airborne communication system may need an ATAlink equipment.

For example, FIG. 15 shows two UAVs 1510 and 1520 with ATA communicationequipment 1515 and 1525 onboard, respectively. Using this equipment, awireless ATA link 1530 can be established between UAVs 1510 and 1520.The wireless ATA link 1530 may be an RF link at any available open bandor frequency, which can be established and supported by a directional RFantenna, included in this example in the ATA communication equipment1515 and 1525. Because the ATA links are dedicated point-to-point links,much higher antenna gain and a lower transmission loss can be achievedin the ATA links as compared to the ATU links. Therefore, the ATAantennas may be substantially smaller, lighter, and less power consumingthan the ATU antennas. Alternatively, the ATA link may be establishedusing a free-space optical (FSO) communication system, which also may bea part of the ATA communication equipment 1515 and 1525. The FSOcommunication system may use a communication grade laser (e.g., asemiconductor laser operating in the wavelength range of 1300-1600 nm)and a high bit-rate optical receiver. The FSO communication systemenables very high bandwidth ATA links, up to 40 Gbit/sec per a singlechannel, and requires less electrical power for its operation incomparison to the ATA RF antennas. For a given net (combined)communication capacity of the ATU link module, i.e. a first capacity,which is given by the sum of individual ATU sections capacities, an ATAlink module may have a net (combined) communication capacity, i.e., asecond capacity, that is at least equal to or greater than the firstcapacity. For example, a system with the 10 Gbit/sec ATU module mayrequire an ATA module with at least 10 Gbit/sec capacity.

In accordance with embodiments of the present invention, FIG. 16 shows aUAV fleet 1600 as a part of a distributed airborne communication system,which includes UAVs 1610-1650. Using onboard ATA link sections the UAVs1610, 1620, 1630, 1640, and 1650 establish ATA links 1615, 1625, 1635,and 1645, which are maintained between the nearest neighbors in the UAVfleet. As a result, a signal from the UAV 1610 can be relayed fromplatform to platform to the UAV 1650 via several ATA links 1615, 1625,1635, and 1645. Alternatively, additional direct ATA links may beestablished if necessary, for example between UAVs 1610 and 1640 toshorten the signal relay path. ATA links may be used for short range (<1km), medium range (1-10 km) and long range (>10 km) signal transmission.In the latter case, they may serve as an alternative to ground-basedtransmission lines, especially in situations where there is no existingground-based communication infrastructure or it is cost prohibitive tocreate a ground-based communication infrastructure. ATA links may beintermittent, i.e., they may be established and maintained on as neededbasis, or they may be permanent depending on the network configuration.Due to respective motion of the aircraft with respect to each other,some or all ATA links may require continuous active tracking and/orrealignment. In order to simplify this, UAVs in a pair involved in theATA link may maintain different altitudes and/or fixed relativepositions to simplify the ATA link tracking and maintenance.

In some embodiments, as shown in FIG. 17, a ground-based gateway station1700 may be provided and used to establish broadband communicationchannels with the UAV fleet above. For this purpose, the gateway station1700 may rely on RF, microwave, and/or optical wireless links, which canbe supported by RF antennas, microwave antennas, and/or FSO apparatus.In addition to antennas and FSO apparatus, the gateway station 1700 mayinclude a network operations module for monitoring and controllingdistributed communication payload onboard of the UAV fleet, acommunication interface for connecting to wired networks (for phone,data and others) on the ground, and facilities to house and maintain allstation's hardware and equipment. The UAV fleet may include one or moreUAVs, such as UAVs 1710 and 1720 shown in FIG. 17. The UAVs 1710 and1720 may carry ATG communication sections 1715 and 1725 as parts oftheir shared communication payload. The ATG communication sections mayalso comprise RF antennas, microwave antennas or FSO apparatus forestablishing ATG links 1730 and 1740 respectively with the gatewaystation 1700. ATG links may be operated as fixed point-to-point linksusing either high-gain directional antennas or FSO apparatus. The ATGlinks 1730 and 1740 may utilize the RF spectrum outside the frequencyrange used for ATU communication links to avoid interference, e.g., inthe range of about 5 to about 100 GHz. These links in this case may beoperated either at the same frequency (using spatial diversity todifferentiate between different UAVs) or at different frequencies. Ineither case, a larger carrier frequency typically provides a largercommunication bandwidth for ATG links. FSO-based ATG links may achieveeven larger communication bandwidths (up to 40Gbps) under suitableweather conditions (i.e., absence of cloud cover). The ATG link modulemay have a net communication capacity (a third capacity) that is atleast equal to or greater than the net communication capacity of the ATUlink module (the first capacity)). For example, a system with the 10Gbit/sec ATU module may have an ATG module with at least 10 Gbit/seccapacity.

In accordance with embodiments of the present invention, FIG. 18 showsan airborne wireless broadband communication system (communicationsystem 1800), comprising a gateway base station 1810, a fleet ofairborne communication platforms (UAV fleet 1820), and communicationcells (ATU ground cell 1840 and ATU air cell 1850). The gateway basestation 1810 may be located on the ground 1805 and establish an ATG link1815 with the UAV fleet 1820, which in turn may be composed of severalUAV platforms 1830 ₁-1830 _(N), where N is the number of UAV platformsin the UAV fleet 1820. The UAV platforms may establish ATA links 1825between each other to relay communications in the system. Furthermore,the UAV fleet 1820 establishes an ATU link 1835 to an ATU ground cell1840 and an ATU air cell 1850 below. The ATU link 1835 enables one-wayand two-way communications with the end-users 1845 located in the ATUground cell 1840 or airborne end-users 1855 in the ATU air cell 1850.Gateway base station 1810, UAV platforms 1830, and end-users are themain nodes in the network provided by the communication system 1800. Thesignals received from the end-users may be relayed through the UAV fleet1820 to the gateway base station 1810, which in turn forwards them tothe signal routing center that determines its final destination. Therouting center may be co-located with the gateway base station 1810.Similarly, the signals originating at the routing center may be relayedthrough the gateway base station 1810 to the UAV fleet 1820, which findsthe corresponding ATU cells and forwards the signals to the appropriateend-users located there. The signal path may also be shortened in somesituations by bypassing some nodes in this network. For example, if thecommunication is between end-users in the same ATU cell or the cellssupported by the same UAV fleet, the communication path may avoid thegateway station, so that the signal may transit more directly and onlythrough the UAV fleet portion of the network.

The communication system 1800 may be modified to include multiplegateway station to increase system capacity. These gateway stations maybe positioned in different locations on the ground and elsewhere inorder to diversify the network design and avoid inter-channelinterference between different stations and corresponding ATG links.Different stations may link to different airborne platforms to shortenthe signal path, or to the same airborne platforms to increaseinformation transfer rate and capacity. Multiple ATU cells (both on theground and in the air) may be produced by the UAV fleet. Some of thecells may cover the area in which the gateway stations are located.Different user types inside the communication cells may be serviced bythe communication system 1800, including (1) individuals via personalmobile communication devices, such as mobile phones, tags and wearableelectronics, (2) autonomous vehicles, such as driverless cars andvarious UAVs equipped with wireless mobile transceivers, (3) groundvehicles with fixed wireless communication apparatus, (4) pilotedaircraft, (5) fixed and mobile ground-based transceivers for commercial,government, municipal, civil, military, emergency and many other uses.

In another embodiment of the invention shown in FIG. 19, a communicationsystem 1900 is provided, which includes an airborne portion comprising aground station 1910, a UAV fleet 1920, and a region with ATU cells 1930.The airborne portion may function in a similar way to that describedabove for the communication system 1800. In addition, there may beadditional ground-based segments of the communication system 1900,including terrestrial wireless and wired networks. For example, aterrestrial wireless cellular network 1940 may be a part of thecommunication system 1900, where it provides an area coverage at leastpartially overlapping with the ATU cells 1930. In these overlappingareas both services (airborne and terrestrial) may co-exist and providecommunication channels to end-users on a co-primary basis. In addition,the UAV fleet 1920 may establish wireless air-to-tower (ATT) links 1945for direct communications between the airborne and terrestrial segments(e.g., as serviced by cell towers, or cellular communication towers) ofthe communication system 1900. Furthermore, a wired broadband network1950 may also be part of the communication system 1900, which areinterconnected via a broadband wired link 1955, as shown in FIG. 19.This network allows end-users to access internet, connect to otherremote networks and communicate with other users serviced by othercommunication systems. Among other things, the communication system 1900also allows, for example, to provide additional (ground-based)connection paths to the terrestrial phone networks, such as theterrestrial wireless cellular network 1940.

In some embodiments of the invention, and as shown in FIG. 20, acommunication system 2000 is provided, which includes a communicationsatellite 2010, a UAV fleet 2020, and a region mapped with ATU cells2030. The communication satellite 2010 is a space-based gateway station,which performs functions in this system similar to those for theground-based gateway stations described above. The communicationsatellite 2010 may orbit the Earth as a part of a larger satellitenetwork, comprising many communication satellites, some or all of whichmay also be able to function as gateway stations. The UAV fleet 2020 maybe able to form air-to-space (ATS) links 2015 using microwave and RFantennas in the frequency range allocated to the satellitecommunications. The UAV fleet may also be able to provide ATU links 2025and service ATU cells 2030 underneath. In some embodiments, acommunication system can include both ground-based and space-basedgateway stations, as described herein, and which are capable ofestablishing additional communication links between themselves. This mayenable introduction of such communication networks and systems intoworld regions, where wired communication network infrastructure does notexist.

In accordance with embodiments of the present invention, FIG. 21 shows adistributed airborne communication payload (payload 2100) for a UAVfleet 2190. In general, the payload 2100 may segmented into functionalpayload segments, which include payload control and managementelectronics 2110, ATU link equipment 2120 (e.g., ATU link module), ATAlink equipment 2130 (e.g., ATA link module), ATG link equipment 2140(e.g., ATG link module), ATT link equipment 2150 (e.g., ATT linkmodule), and ATS link equipment 2160 (e.g., ATS link module). Some ofthe functional payload segments may be optional, such as for instancethe ATT link equipment 2150 and ATS link equipment 2160. Some or all ofthe functional payload segments may in turn be subdivided into smallersections: for example, the ATU link equipment 2120 may be subdividedinto X parts, referred to as ATU link equipment 2120 ₁-2120 _(X), whereX is in the range of 1 to N (and N is the number of UAVs in the UAVfleet 2190).

The subdivided, smaller sections of the functional payload segments maybe distributed and mounted onto the individual UAVs in the UAV fleet2190. For example, each functional payload segment may be divided into Nequal sections and evenly distributed among N UAVs, so that a UAV 2190_(i) contains functional payload sections 2110 _(i)-2160 _(i) (i rangesfrom 1 to N). In this case, the UAVs comprising the UAV fleet aresimilar to each other in capabilities and functionalities, whichincreases system redundancies and robustness. Alternatively, some or allof the functional payload segments may be unequal and dissimilar intheir physical and operational characteristics. As a result, the payload2100 distribution across the UAV fleet 2190 may be uneven, so that atleast some of the individual UAVs may differ from each other in thiscase. This system design approach allows some of the UAVs to be morespecialized and potentially more efficient in performing one or morefunctions within the airborne communication system, such as transmittingsignals; receiving signals; linking with users, gateway stations, andairborne platforms; processing voice, text, network messaging, and data;tracking system status; synchronization and management of individualnetwork elements; and so on.

In accordance with embodiments of the present invention, FIG. 22 showsan airborne RF link equipment subsystem 2200, which may be used toimplement RF-based communication links describe above. It comprisesparts and components that may be included in either ATU link equipment2120, ATA link equipment 2130, ATG link equipment 2140, ATT linkequipment 2150, or ATS link equipment 2160. The airborne RF linkequipment subsystem 2200 may include an antenna 2210, a power amplifier2220, a transceiver 2230, and a baseband interface 2240. As any part ofa communication payload, these parts of the airborne RF link equipmentsubsystem 2200 may be further subdivided into smaller sections (orblocks) as shown in FIG. 22, each one to be carried by an individualUAV. For example, sections 2210 _(i), 2220 _(i), 2230 _(i) and 2240 _(i)may be combined into a single segment, such as 2120 _(i) (as well as2130 _(i), 2140 _(i), 2150 _(i), or 2160 _(i)), and mounted on board ofa single UAV, such as UAV 2190 _(i), where i ranges from 1 to N. Thesesections (2210 _(i), 2220 _(i), 2230 _(i) and 2240 _(i)) may be wiredand interconnected electrically on board a UAV and also connected to itspower train subsystem. On the other hand, interconnection andcommunication between different sections of any segment of the payloadlocated on different UAV platforms (e.g. 2110 ₁ and 2110 ₂, or 2120 ₁and 2120 ₂) may be done wirelessly via ATA links. Although each part ofthe airborne RF link equipment subsystem 2200 is shown subdivided intoequal numbers of smaller sections, different parts of the airborne RFlink equipment subsystem 2200 may be subdivided into different numbersof smaller sections or not subdivided at all.

Conventional wisdom in system design is to conserve hardware and reusecomponents to perform multiple functions in order to make the systemmore efficient and of simpler design. For example, a communicationsystem with a single phased array antenna is capable of producingmultiple RF beams and thus serving multiple communication links (e.g.,multiple ATU cells). From any conventional approach, the same systembroken into smaller constituent parts with multiple phased arrayantennas would be less efficient, more complex, and therefore lessdesirable. However, when considering airborne communication systems,such as those described above, the inventors discovered thatconventional rules do not always apply. For example, the inventors findthat payload power consumption can be a far more demanding condition anda more difficult specification to meet than the payload weight for theUAV platform. The inventors also find that the payload power consumptiondepends primarily on the communication system capacity, utilization, andinformation transfer rate. Therefore, there is little or no penalty onthe payload power consumption when such a system is subdivided intosmaller parts. Furthermore, even the weight penalty associated with suchsubdivision is minimized, because the weight of an RF antenna is in partproportional to its RF signal load, i.e., the net RF current produced byits power amplifiers. On the other hand, the inventors find that thebenefits of a distributed communication payload far outweigh anydrawbacks. When considering the overall efficiency of a combinedairborne system, i.e., the payload and the UAV platforms, the efficiencyof a fleet of UAVs with a distributed payload exceeds the efficiency ofa single UAV with a solitary payload. This comes as a result of ascaling law for large aircraft (or any other 3-dimensional object),stating that the weight of a UAV tends to be proportional to the thirdpower of its size. On the other hand, the weight of a UAV fleet islinearly proportional to the number of UAVs. Consequently, for the samecapacity the weight of a single-UAV-based communication system is muchlarger than the weight of a UAV-feet-based communication system.Therefore, the latter is more efficient and more advantageous forairborne communications.

Although a distributed payload may be physically located on board ofdifferent airborne platforms, from the network standpoint it stillrepresents a single network component, e.g., a single node. Theend-users and network operators interact with a whole UAV fleet and itscommunication payload, rather than individual components. They see asingle interface and a single system image, as if the distributedpayload is a single entity, and consequently they are unable todistinguish its constituent parts, i.e., any subdivisions in thepayload. To accomplish this task, the payload control electronicsinternally manage and coordinate the operations of each payloadcomponent by using specialized computer cluster middleware. FIG. 23shows a payload control module 2300, which may include control sections:an administration section 2310, a cluster database 2320, an eventhandler 2330, a task scheduler 2340, and a block controller 2350. Theblock controller 2350 controls blocks (i.e., sections) of other payloadmodules, e.g., a section of an ATU link module. Such a payload controlmodule is a subsystem similar to a computer cluster in that it hasseveral distinct and separate hardware parts (akin to computer nodes),that are run by a distributed algorithm software and working togethersynchronously or asynchronously on shared tasks. The administrationmodule 2310 enables real time monitoring of payload modules and fullaccess to the software and data loaded on control module sections. Thecluster database 2320 stores, provides, and continuously updates variousdata types necessary for airborne communication payload operations, suchas cellular mapping data, end-user positioning, gateway positioning,individual UAV positioning, subsystem statuses, and so on. The eventhandler 2330 provides asynchronous subsystem control capabilities, whereany subsystem may request attention for a service at any time, e.g., inan event of a malfunction or a software-triggered conflict. The taskscheduler 2340 may be used to manage available resources for all onboardsubsystems, schedule and synchronize various tasks, and providestatistical analysis and prediction for future resource allocations. Theblock (i.e. section) controller 2350 may be used to micro-manage theoperations of individual sections and subsystems. All or some of thecontrol modules may operate in parallel.

The distributed payload operations also require communication channelsdedicated to internal communications between individual UAVs. Such achannel (or multiple such channels) may be supported by the ATA linkequipment. Thus, the ATA link equipment may be also subdivided into twosegments—each for internal and external communications, respectively, asshown in FIG. 24. The ATA subsystem 2400 comprises at least twosegments: an ATA control channel 2410 and an ATA relay channel 2420. TheATA control channel 2410 serves the internal needs of the payloadcontrol module 2300, by providing fast, broadband communications linksbetween control sections on different UAVs, i.e., cluster elements. TheATA control channel enables the distributed computing operation of thepayload control module 2300 as a whole and its different segments andsections. The ATA relay channel 2420 serves as a conduit for allexternal network traffic between platforms within the UAV fleet, whichincludes text messaging, phone calls, data transfers, internet browsing,video and radio streaming, broadcasting, multicasting and so on. The ATArelay channel 2420 may require a substantially broader communicationbandwidth than the ATA control channel 2410 to accommodate all networktraffic transiting trough the network. The two channels may be operatedcompletely separate from each other, for example by using different RFranges or by using different types of ATA links, such as radio links forthe ATA control channel and FSO links for the ATA relay channel.

The ATA control channels enable formation of an airborne local areanetwork cluster, where the cluster elements include individual sectionsof the payload control module. The internal network architecture of sucha cluster may be either centralized or decentralized. In the formercase, the configuration of internal wireless connections between clusterelements is fixed, so that internal signal routing and messaging ismanaged by one or more payload control sections, i.e., a networkcontroller (e.g., an administration section 2310). In the latter case,the airborne cluster may adopt an ad hoc network configuration, in whicheach cluster element may take part in signal routing, resulting in amuch more dynamic architecture. Both approaches have their advantages.The centralized cluster operation may reduce response time and increasesystem capacity. On the other hand, the decentralized cluster operationmay increase system redundancy and reliability.

In accordance with embodiments of the present invention, FIG. 25 shows adistributed airborne communication network 2500 comprising severalnodes: an end-user node 2510, an airborne node 2520, a gateway node2530, an external node 2540, a cell tower node 2550, and a satellitenode 2560. The cell tower node 2550 and the satellite node 2560 may beoptional, as indicated by the dotted arrows. Several networkconfigurations are possible, in which some of these nodes may be absentor some of these nodes may be present in quantities greater than one.For example, a minimum successful distributed airborne communicationnetwork requires only two nodes: the end-user node 2510 and the airbornenode 2520. On the other hand, larger networks may include multipleend-user nodes, airborne nodes, gateway nodes, and others. The end-usernodes may be based on the ground, in the air space, or both. Thecommunication flow in the distributed airborne communication network2500 may occur as follows. A signal from the end-user node 2510, e.g., acell phone, is transferred via a wireless link 2515 to the airborne node2520. The airborne node 2520 relays the signal to the gateway node 2530via a wireless link 2535, which then forwards it to the external node2540 via a wired connection 2545. The external node 2540 provides aninterface with external networks, which may route the end-user signal toits final destination (in this scenario outside the distributed airbornecommunication network 2500). Upon receiving a response, another signalmay be forwarded in the opposite direction as follows. The external node2540 using a link 2546 transfers the response signal to the gateway node2530, which in turn sends it to the airborne node 2520 via a link 2536.The airborne node 2520 then finds the end-user and forwards the signalto the end-user node 2510 via a link 2516. Of course, both of thesetransfer processes may occur simultaneously without interference fromeach other. Although the internal operations of the airborne node 2520are opaque and invisible to the end-user, they involve additional signaltransfers via wireless links 2525 and 2526 between individual UAVplatforms 2520 ₁, 2520 ₂, . . . and 2520 _(N), where N is the number ofUAVs in the airborne node 2520.

In accordance with embodiments of the present invention, FIG. 26 shows adistributed airborne communication network 2600 comprising severalnodes: a plurality of airborne nodes 2610, 2620, and 2630, and aplurality of end-user nodes 2615, 2625, and 2635. Of the plurality ofend-user nodes 2615, 2625, and 2635, at least one end-user node may beground-based and at least one end-user node may be airspace-based). Thenodes are interconnected by ATA links 2650 and ATU links 2660. Theairborne nodes are provided by different distributed communicationpayloads carried by different UAV fleets. The ATA links 2650 are used tointerconnect the UAV fleets, payloads, and associated nodes similarly tothe way individual UAVs are linked within a fleet. The ATU links 2660provide end-user links in end-user node areas assigned to the respectiveairborne nodes as described above. The number of end-user nodesassociated with an airborne node may be greater than one. Also, thenumber airborne nodes in the distributed airborne communication network2600 may be any number greater than one (i.e., not just three nodesshown in FIG. 26). The airborne nodes may be similar to each other, oralternatively may be different in size, number, altitude, endurance,capabilities, and so on. Similarly, the end-user nodes may also bedifferent from each other in their scope, size, and shape, which ingeneral depends on the ground terrain, population density anddistribution, roads and traffic patterns, end-user types, etc.

Airborne node operations, i.e., the operations of a distributedcommunication payload on board of a UAV fleet, may be optimized byproviding a degree of functional division among its constituentcomponents and associated UAV platforms. Such a division orspecializations among different UAVs in a fleet may be reflected intheir hardware, software, or both. On the hardware side, UAVs may differin their airframes, power systems, propulsion systems, payload contents,payload design, or payload distribution and location. On the softwareside, even UAVs with identical hardware design and payload compositionmay differ in software content and the types of functions theyspecialize within the fleet. Different UAV specializations may beattractive for optimization of the airborne node operations, such asreceiver UAVs, transmitter UAVs, relay UAVs, master UAVs, slave UAVs andso on. Functional subdivision is possible not only in the physical layerof the airborne network, but also in its logical layers. Some UAVs mayspecialize in organizing transport layers, network routing, datapackaging, etc. Optionally, one or more UAVs may perform one or morebase station functions, e.g., by enabling direct signal routing betweenend users in the same service area without passing through a gatewaystation. Consequently, various airborne node topologies may be possibleif its constituents can be specialized in one or more functions.

In accordance with some embodiments of the present invention, FIG. 27shows an airborne node design topology 2700, which includes three typesof payload bearing UAV platforms: a relay platform 2710, a transmitterplatform 2720, and a receiver platform 2730. The relay platform 2710comprises a section of the communication payload, which interfaces otherUAVs, fleets of UAVs, gateway stations and other external nodes, andrelays signal between them via wireless links 2705, 2715, and 2725. Thetransmitter platform 2720 comprises a section of the communicationpayload, which defines a communication cell on the ground and in the airbelow and transmits signals to the end-user inside the cell via awireless link 2735. The receiver platform 2730 comprises a section ofthe communication payload, which also defines a communication cell onthe ground and in the air below and receives signals from an end-userinside the cell via a wireless link 2745. The communication cellsdefined by the transmitter platform 2720 and the receiver platform 2730may be the same in size and shape and cover the same geographical area.Alternatively, they may be different from each other. In this case, forexample a receiver cell may be twice the size of the transmitter cell,so that an airborne cell may include two transmitter platforms and onereceiver platform with the combined size of the two transmitter cellsequal to the size of the receiver cell.

In accordance with some embodiments of the present invention, FIG. 28shows another airborne node design topology 2800, which includes twotypes of payload bearing UAV platforms: a master platform 2810 and aplurality of slave platforms (only slave platforms 2820 and 2830 areshown in FIG. 28). The master platform 2810 houses the major portion ofthe payload control module (i.e., a master section of the distributedcommunication payload) that manages and operates the slave platforms(each having slave sections of the distributed communication payload).The slave platforms, such as slave platforms 2820 and 2830, may containthe majority of the ATU, ATA, and ATG equipment sections. The masterplatform 2810 communicates directly with network operators via awireless link 2805 and controls the slave platforms 2820 and 2830 vialinks 2815. The slave platforms 2820 and 2830 may communicate withend-users and among themselves using ATU links 2825 and ATA links 2835,respectively. This design approach may be attractive, because itsimplifies the software necessary to run both the master and slaveportions of the payload control module, and it also may simplify theairborne network design and its maintenance.

The airborne node topology may be flexible, adjustable andreconfigurable. The same UAV may be able to perform different functions,so that it may play different roles in the node. For example, the sameUAV may be able to function as either a receiver UAV, a transmitter UAVor both. This can be accomplished by using for example multi-purposepayload modules, sections, and general subsystems, such as an RF antennaconfigurable to operate in both transmitter and receiver modes. Theparticular role this UAV plays in any given node may be chosen atrandom, depending on many factors including the overall node topology,UAV statuses, channels loading, weather and so on. In addition, theoverall node topology may be changed depending on these factors anddecisions of network operators. For example, the size of the node andits capacity may be increased by adding more UAVs in response toincreased demand. New frequency bands and communication capabilities maybe added by incorporating additional UAVs with specialized equipment andfunctionality. Upgrades and repairs can be made on individual UAVswithout bringing the whole fleet down. A special loitering fleet ofback-up UAVs may be used in the vicinity of operating airborne nodes toshorten the response time in case of emergency or sudden jumps incommunication traffic. Also, the node topology may be changed withoutchanging the number of UAVs in the fleet, by reassigning the roles ofindividual UAVs, e.g., in switching from the airborne node designtopology 2700 to the airborne node design topology 2800.

In regard to the airborne node design topology, the inventors also notethat the distributed payload approach enables network providers tobetter match the network capacity to the existing demand from end-usersby managing channel loading. The customer demand for communicationbandwidth, i.e., the information transfer rate, varies from day to day,hour to hour. For example, this demand typically peaks during daytimeand decreases at night. When the demand decreases the airborne systementers the regime of substantial overcapacity. It is advantageous for anairborne system to reduce its capacity in order to maintain operationalefficiency and maximize system endurance. Because the power consumptionof idling hardware or hardware operating at low loads is stillsubstantial, it is attractive to completely shut down some sections orsubsections of the system, such as high-power RF transceivers, whileoperating at high channel loading and close to maximum capacity onremaining sections. For example, a fleet of 10 UAVs with 10 ATU antennasmay be able to operate more efficiently at night with only five workingantennas at any given time. This approach allows five other UAV tocompletely shut down their payload sections to conserve power. TheseUAVs may alternate their roles by for example changing their statusesbetween active and inactive every hour and thus improve overall systemefficiency. The number of UAVs in the fleet above was used only forillustration; this principle can be applied to a fleet with any othernumber of UAVs greater than one. It is also possible to do the reverse,where upon increase in traffic the UAV fleet may grow in size bybringing in additional payload-bearing aircraft. The additional UAVs maybe brought in from other fleets, idling back-ups, and the ground base.

Operations of a distributed airborne wireless system also requirecareful flight control of a fleet of airborne platforms. In accordancewith embodiments of the present invention, FIG. 29 shows a UAV fleet2900 comprised of 5 UAVs 2910. Of course, a UAV fleet may contain anynumber of aircraft greater than one. In addition to its payload, eachUAV 2910 has dedicated flight control electronics (see, e.g., flightcontrol electronics 310 in FIG. 3). One of its functions is to provideeach UAV with situational awareness and prevent mid-air collisionsbetween different UAVs inside the fleet. The UAV flight controlelectronics establish a protective region 2920 (i.e., a virtual bubble)around the UAV, which is considered off limits to other aircraft. Theregion may be established for example using specialized software andUAV's GPS data; the software then may broadcast the protective region'scoordinates to the fleet members for collision avoidance. In addition,the flight control module may include proximity sensors to furtherimprove collision avoidance capabilities against malfunctioning UAVs andflying objects outside of the UAV fleet.

The flight patterns of each UAV 2910 in the UAV fleet 2900 may besimilar to or different from each other. Each UAV may have a preloadedflight plan that describes in details the flight trajectory it has tofollow. The flight may be updated periodically from the ground bynetwork providers or modified autonomously by the flight control andpayload control electronics. The flight plan may be the same for eachUAV, so that the UAVs may fly together synchronously and maintain thesame speed and distances from each other. This approach simplifies ATAlink maintenance and payload synchronization across the fleet.Alternatively, the flight plans may be different and subject to changefor each UAV, which improves system robustness and reduces itssensitivity to external perturbations (e.g., rough weather, turbulence,etc.). The flight plan may include circling and hovering in the airspace above the designated communication cells. Thus, the cellboundaries may define the boundaries of the UAV flight plan. In tightfleet formations with very closely spaced UAVs, a special synchronizedflight pattern may be used that may be controlled from a master flightcontroller on board of a master UAV platform.

The flight paths of some or all of the UAVs 2910 may be planned in sucha way that at least some of these UAVs may be able fly in the air streamwake of other UAVs within the fleet 2900. For example, the UAV 2910 ₂may be able to fly behind the UAV 2910 ₁ in sufficient proximity toreduce aerodynamic drag and increase lift of its airframe, whilereducing propulsion power necessary for maintaining a level flight. Thiseffect is made possible by the tip vortices produced by the forward UAV2910 ₁. It is known from flight patterns and formations used by birdsand fish that 15% or more of mechanical energy can be conserved in sucha way. Similarly, UAV formations of two or more aircraft may be used toconserve energy and substantially reduce power requirements in longendurance flights. The UAV flight pattern and formation may be eitherpersistent, i.e. substantially unchanging over long periods of time(hours, days, weeks, or months), or intermittent, i.e., varying andadaptable to specific environmental conditions, working situations andfleet statuses. In the latter case, for example, one or more formationflight patterns may be used only at night or during winter solstices,when power conservation is most important. Alternatively, there may beat least two different flight formations each optimized for day andnight time operations, respectively.

Flight power reduction may be achieved when at least two UAVs are flyingclose to each other as shown in FIG. 30. The UAV 3010 ₁ produces a wakebehind its wing tips, which may be used by the UAV 3010 ₂ for flightpower reduction. Both UAVs may be substantially within the samehorizontal plane, although the effect may still be observed even withsome vertical offset between the UAVs. Also, the tail UAV 3010 ₂ may belaterally offset with respect to the front UAV 3010 ₁, as shown in FIG.30. The effect may be observed and used over a range of distancesbetween the two UAVs. The shortest distance 3021 is in part determinedby the aircraft safety range, e.g., the protective region 2920 in FIG.29, the onboard flight control electronics capabilities, e.g., theautopilot specifications, and other factors. The longest distance 3022is determined by the wake size and strength. Both distances can bemeasured in terms of the UAV's wing span. For example, the shortest safedistance may be equal approximately one wing span, while the longestdistance may be equal to a few tens (e.g., about 10-50) of the UAV'swing spans.

FIG. 31 shows a few other examples of flight formation patterns for UAVfleets. Formations 3110 and 3120 are V-shaped formations of differentsizes (with 3 and 5 UAVs respectively), in which the wake of a leadingUAV is used by one or more tailing UAVs. Formations 3130 and 3140 areinverted V-shaped formations, in which a tailing UAV may use at leasttwo wakes from leading UAVs. This way it is possible to significantlyreduce propulsion power consumption of the tailing UAVs by at leasttwice the amount possible in the formations 3110 and 3120, which may beimportant for working situations requiring increased payload powerconsumption from the tailing UAVs. Formations 3150 and 3160 are hybridformations, which share some of the features with both V-shaped andinverted V-shaped formations. Of course, other formations with differentnumber of UAVs are also possible.

In accordance with embodiments of the present invention, the UAV fleetsmay maintain communication and computing payloads on station ataltitudes above cloud cover even during the longest nights and dimmestdays of winter at temperate latitudes. (e.g., at NY, San Francisco,Beijing, Tokyo, latitude ˜40, or the like). In such embodiments, the UAVfleets may be powered at least in part by renewable solar energy. Insummer time or any time in tropical latitudes, these UAV fleets haveapproximately 2.5 times more solar energy available to them. Excessenergy can be used to provide additional services. In some embodimentsof the present invention, internet and computational servers arecollocated in UAV fleets, some of which fly over tropical latitudes ormigrate seasonally to mitigate winter conditions. At the target flightconditions between 15 and 25 km, air temperature is roughly ˜40 degreesCelsius, air velocity will be roughly 100 km/hr, and average insolationoften greater than 40% peak over ground level, because of absence ofcloud cover. Therefore, collocation of computational servers (such ascloud servers) in summer UAV fleets will be more economic thanterrestrial server farms with air conditioning, leased floor space, andexternal network fees. This economic advantage will accelerate as solarpower with battery storage achieves grid parity, and UAV fleets flyglobally. Collocation of communication and computational services in UAVfleets also improves speed relative to prior art terrestrial services,since free space optical and radio ATA links have transmissionvelocities approximately 1.5 times greater than fiber optics.

In accordance with embodiments of the present invention, the size andextent of an airborne wireless communication node, i.e. a UAV fleet, maybe determined by several factors, including application requirements,individual UAV specifications and capabilities, payload distribution,safety regulations, regional specifics, renewable energy resourcesavailable and so on. In any case, the size of the fleet is given by themaximum separation in the horizontal plane between any two UAVs withinthe fleet, which in turn may be referenced and compared to the size ofcorresponding communications cells as produced on the ground by one ormore UAVs. FIG. 32 shows a distributed communication system 3200comprising a fleet of two UAVs 3221 and 3222, which service a singlecommunication cell 3210. The size of this fleet as determined by thedistance between UAVs 3221 and 3222 may be smaller than the size of thecommunication cell 3210. This distance may be determined by either theATA communication link distance, the most optimal separation for flightformation, weather conditions or other factors and combination thereof.This distance may be also smaller than the average altitude of the UAVfleet. For example, the UAVs may be less than 1 km apart, while flyingat an altitude of 20 km and producing a cell of 10 km across.Constituent UAVs in the distributed communication system 3200 mayperform similar or alternatively different functions. For example, theUAV 3221 may function as an ATU transmitter and the UAV 3222 mayfunction as an ATU receiver within the same communication cell 3210.

In accordance with embodiments of the present invention, FIG. 33 showsanother exemplary embodiment of a distributed communication system 3300comprising a fleet of two UAVs 3321 and 3322, which service twodifferent communication cells 3311 and 3312, respectively. The size ofthis fleet as determined by the distance between UAVs 3321 and 3322 maybe smaller than the combined size or extent of communication cells 3311or 3312. It may be smaller than the size of either communication cells3311 or 3312 (i.e. the diameter of a cell for a round cell). It may bealso smaller than the average separation between the communication cells3311 and 3312 (i.e. the distance between the cell centers). The UAVfleet may be positioned directly above one of the cells, the overlappedregion between the cells or sideways with respect to either of the cellsas shown in FIG. 33.

In accordance with embodiments of the present invention, FIG. 34 showsanother exemplary embodiment of a distributed communication system 3400comprising a fleet of two UAVs 3421 and 3422, which service twodifferent communication cells 3411 and 3412, respectively. In this case,the fleet size may be similar or larger than the size of the respectivecommunication cells or separation between the cells. It may bepreferable in this case to position each UAV directly above acorresponding communication cell as shown in FIG. 34. UAVs in thedistributed communication systems 3200, 3300 and 3400 may produce andservice more than one communication cells. Furthermore the number ofcommunication cells these UAVs service may be different from each other.Furthermore, some UAVs may be used for providing ATG links, in whichcase the fleet size may be compared to the distance between theground-based gateway station and the UAV fleet. The UAV fleet with adistributed communication payload may be smaller in its extent incomparison to the average distance to its gateway station.

In accordance with another aspect of the present invention, FIG. 35shows a method 3500 for communicating using a distributed airbornewireless system. The method 3500 includes receiving an end-user signalby a distributed payload at 3510, for example from an end-user in aground cell or air cell as described above. Receiving the end-usersignal may be enabled by the use of ATU link equipment to providewireless links between UAVs and end-users. Next, the end-user signal maybe relayed along the distributed payload at 3520, for example, within aUAV fleet, between UAV fleets, or as otherwise described above. Relayingthe end-user signal may be enabled by the use of ATA link equipment,providing wireless links between different UAVs. Optionally, theend-user signal may be transmitted to the ground gateway station or toanother end-user on the ground and/or surrounding airspace at 3530, ifrequired. The link to the ground gateway station may be provided usingATG communication equipment. Additional actions are also possible, suchas receiving and transmitting signals from/to communication satellites,other aircraft, terrestrial cellular stations, other airborne wirelesssystems and so on.

Furthermore, another method of communicating using such a systemincludes a method of transmitting a signal to the end-user, which is thereverse of the process described in FIG. 35. For example, the method maybegin by receiving a signal to be transmitted to an end-user from theground gateway station. Next, the signal may be relayed along thedistributed payload. Lastly, the signal may be transmitted to theground-based gateway station for ultimate routing to other end-users oralternatively it may be routed directly to another end-user withoutpassing through the gateway station.

In accordance with another aspect of the present invention, FIG. 36shows a method 3600 for providing a distributed airborne wirelesscommunication node. The method 3600 includes estimating applicationrequirements for an overall communication payload within a given servicearea, as indicated at 3610. Next, as indicated at 3620, a UAV fleet isprovided that is comprised of a number of UAV platforms with a netpayload power and weight capabilities that are equal to or greater thanthe specified communication payload power and weight requirements,respectively. Finally, as indicated at 3630, the specified communicationpayload is subdivided into payload sections, so that each section may bemounted on a single UAV platform with power and weight requirements thatare equal to or less than payload power and weight capabilities of arespective UAV platform. Subdividing the payload into separatefunctional sections may be accomplished without sacrificing the overallfunctionality of the payload as a whole. Subdividing the payload intoseparate functional sections also takes into account an overhead (apenalty from additional weight and power requirements) resulting fromadditional intra-node communications between individual UAVs in thefleet.

Furthermore, the method 3600 may include several additional or optionalactions as shown further in FIG. 36. For example, as indicated at 3640,the method 3600 may further include providing additional equipment forATA communications between individual UAVs within the fleet, hardwareand software for organizing and synchronizing operations of individualUAVs, a node controller and other elements for regulating nodeoperations. The method 3600 may also include launching the fleet intoairspace, transporting the fleet to the service area, distributing thefleet within the service area for best coverage and performance, asindicated at 3650. UAVs may be launched and transported simultaneouslyand concurrently or non-simultaneously and separately. Furthermore, themethod 3600 may include providing auto-pilot capabilities to one or moreUAVs within the fleet, which enable cooperative flight patterns,collision avoidance, formation flights, more efficient wind or solarenergy harvesting (e.g., as described in above-referenced U.S. Pat. No.8,448,898) and so on, as indicated at 3660.

In accordance with yet another aspect of the present invention, FIG. 37shows a method 3700 for providing a distributed airborne wirelesscommunication node. The method 3700 includes providing a number of UAVplatforms with fixed predetermined payload capabilities, such as payloadpower, weight, operating temperature, and so on, as indicated at 3710.Next, the method 3700 includes providing a range of communicationpayload sections with requirements that can be satisfied by thecapabilities of a single UAV platform, as indicated at 3720. Some ofsuch payload sections are illustrated in FIG. 4, which may includesections of ATU, ATA, and ATG link equipment, as well as sections of acommunications control module. Finally, the method 3700 includesmounting payload sections onto UAV platforms and forming a UAV fleetwith net communication payload capabilities of an airborne wirelesscommunication node, such as acceptable data/voice formats, maximum datatransfer rates, ground cell coverage area, maximum link range, maximumnumber of users, user density, and so on, as indicated at 3730. The netpayload capabilities can be deduced and estimated from the sum of thecapabilities of its constituent sections. In some embodiments,application requirements for a network node may exceed capabilities ofany single payload section. As a result, a single UAV may not be able toprovide a fully functional node, so that a UAV fleet may be requiredgiven the limited capabilities of a single UAV platform and the superiorcapabilities of a UAV fleet.

In accordance with another aspect of the present invention, FIG. 38shows additional actions (generally labeled 3800), which couldcompliment methods 3600 and 3700. Such actions include subdividing theground area and the airspace area around and below the UAV fleet intocommunication cells, thus producing an airborne cellular map, asindicated at 3810; assigning communication payload sections torespective communication cells and providing communication services(e.g., ATU links) within the communication cells by respective payloadsections, as indicated at 3820; selecting frequency bands, channels andformats for ATU communications within the communication cells tooptimize ATU link performance and minimize interference betweenneighboring cells, as indicated at 3830; maintaining boundaries of eachcommunication cell and the overlap zones or regions between neighboringor overlapping communication cells, as indicated at 3840; changing theat least one of the size, shape, or position of one or morecommunication cells (including elimination of one or more communicationcells from the cellular map), as indicated at 3850; and supportingcommunication services within existing communication cells establishedby terrestrial wireless providers, as indicated at 3860.

The process of cellular subdivision and mapping of the ground area andsurrounding airspace may include coordination with existing cellularmaps from terrestrial and other airborne wireless service providers. Inaddition, airborne cellular mapping may be correlated with otherterrestrial infrastructure, such as road maps, town maps, populationdensity distributions, ground vehicle traffic patterns and so on. Theprocess of assigning payload sections to particular cells (and viceversa) may include selecting ATU link equipment sections for ATU uplinkand downlink, respectively. One cell may be serviced by multiple payloadsections carried by multiple UAV platforms. Alternatively, an ATUpayload section on a single UAV platform may service multiple cells,using for example a phased array antenna.

The process of frequency, channel, and format section within each cellmay be used to optimize airborne node performance by minimizinginterference from neighboring cells, existing wireless systems, andother potential sources of radio transmission noise. It may, forexample, include a method of selecting different frequency bands atneighboring cells separated by a number of frequency guard bands (atleast one). This process may also include satisfying the requirements oflocal and national authorities in charge of regulating wirelesscommunications in the service area (e.g., choosing frequencies onlywithin the allocated RF spectrum).

The process described at 3840 may be used to maintain a fixed orconstant airborne cellular map. Alternatively, the cellular map may beflexible and variable in response to changes in the demand forcommunication services within the service area. For example, in responseto changes in demand, the cellular map may be re-drawn and optimizedeither from a ground-based control station or using an airborne nodecontroller. The airborne node controller may be either a central masterserver computer located on one of the UAV platforms or a distributedsystem of control nodes located on several UAV platforms. The changes inthe size, shape, number, and positions of communication cells may occuron different time scales: minor changes (e.g., boundary adjustments) mayoccur and repeat every minute or so, while major mapping changes (e.g.,cell number reduction) may occur only every 12 hours or more. Inaddition, the airborne node controller may produce different cell mapsin different seasons, i.e., different maps for winter, spring, summer,and fall.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof.

1. A method of providing wireless communication services, comprising:receiving a radio frequency (RF) signal from a first area by adistributed airborne communication payload, wherein the distributedairborne communication payload is comprised of sections located onrespective ones of a plurality of airborne platforms, wherein thesections of the distributed airborne communication payload combine tofunction as a single network component; relaying the RF signal along thesections located on different airborne platforms; and transmitting theRF signal to a second area.
 2. The method of claim 1, wherein relayingthe RF signal further comprises: transmitting the RF signal betweendifferent airborne platforms of the plurality of airborne platforms. 3.The method of claim 1, wherein at least one of the first area or thesecond area is on the ground.
 4. The method of claim 1, wherein thefirst area and the second area are on the ground.
 5. The method of claim1, wherein at least one of the first area or the second area is in theair.
 6. The method of claim 1, wherein one of the first area or thesecond area is on the ground and the other of the first area or thesecond area is in the air.
 7. The method of claim 1, further comprising:using the distributed airborne communication payload, transmittingsignals to and receiving signals from a base station on the ground. 8.The method of claim 1, further comprising: using the distributedairborne communication payload, transmitting signals to and receivingsignals from a cell tower.
 9. The method of claim 1, further comprising:using the distributed airborne communication payload, transmittingsignals to and receiving signals from a communication satellite.
 10. Themethod of claim 1, wherein using the distributed airborne communicationpayload provides a single system image to end-user devices.
 11. Themethod of claim 1, further comprising: providing the wirelesscommunication services for at least 24 hours.
 12. The method of claim 1,further comprising: providing the wireless communication servicesyear-round.
 13. The method of claim 1, further comprising: providingcell phone services using the distributed airborne communicationpayload.
 14. The method of claim 1, further comprising: providingbroadcasting services to the at least one of the first and second areas.15. The method of claim 1, further comprising: estimating applicationrequirements for the distributed airborne communication payload withinat least one of the first and second areas to define a specifiedcommunication payload; providing a fleet comprised of multiple airborneplatforms with a net payload power and weight capabilities that areequal to or greater than the power and weight requirements of thespecified communication payload; and subdividing the distributedairborne communication payload into payload sections with power andweight requirements that are equal to or less than payload power andweight capabilities of a single airborne platform, so that each sectionmay be mounted on a respective airborne platform.
 16. The method ofclaim 1, further comprising: providing a plurality of airborne platformswith predetermined payload power and weight capabilities; providingcommunication payload sections, wherein each section has power andweight requirements that can be satisfied by the capabilities of atleast one single airborne platform; and mounting payload sections ontothe airborne platforms and forming an airborne fleet with netcommunication payload capabilities of an airborne wireless communicationnode.
 17. The method of claim 1, further comprising: providing equipmentfor air-to-air communications between individual airborne platforms,hardware and software for organizing and synchronizing operations ofindividual UAVs, and a node controller for regulating node operations.18. The method of claim 1, further comprising: launching the airborneplatforms into airspace, transporting the airborne platforms to aservice area, and distributing the airborne platforms within at leastone of the first and second areas.
 19. The method of claim 1, furthercomprising: providing auto-pilot capabilities to at least one airborneplatform and enabling at least one of: cooperative flight patterns,collision avoidance, formation flights, or more efficient wind or solarenergy harvesting.
 20. The method of claim 1, further comprising:subdividing at least one of the first and second areas intocommunication cells and producing an airborne cellular map; assigningcommunication payload sections to the respective communication cells,establishing communication links and providing communication serviceswithin the cells by respective payload sections; and selecting frequencybands, channels and formats for communications within the cells tooptimize performance of the communication links and minimizeinterference between neighboring cells.
 21. The method of claim 20,further comprising: maintaining boundaries of the communication cellsand controlling at least one of the number, size, shape, or position ofone or more communication cells.
 22. The method of claim 1, furthercomprising: supporting communication services within existingcommunication cells established by terrestrial wireless providers. 23.The method of claim 1, further comprising: flying the airborne platformsat a first distance from the first area, wherein the distance between atleast two airborne platforms is substantially smaller than the firstdistance.
 24. The method of claim 1, further comprising: flying theairborne platforms at a second distance from the second area, whereinthe distance between at least two airborne platforms is substantiallysmaller than the second distance.
 25. The method of claim 1, furthercomprising: flying at least two of the airborne platforms in a flightformation, wherein at least one of the airborne platforms flies in thewake of another airborne platform.
 26. The method of claim 1, furthercomprising: using renewable power resources to provide electrical powerto the airborne platforms, including at least one of solar power, windpower, or thermal power.
 27. The method of claim 1, further comprising:using free space optical apparatus for communications between theairborne platforms. 28-29. (canceled)
 30. The method of claim 1, furthercomprising: using a piloted airborne platform to perform one ofreceiving signals from, transmitting signals to, or providing auxiliarypower to other airborne platforms.
 31. The method of claim 1, whereinthe sections of the distributed airborne communication payload performat least one same function of receiving or transmitting RF signals. 32.The method of claim 2, wherein the RF signal transmitted between thedifferent airborne platforms is used to control operation of thesections of the distributed airborne communication payload.